Test apparatuses are known for functional testing and monitoring of the response characteristics and tripping characteristics of differing protective relays, in particular frequency relays, distance relays, directional relays and power relays. Such test apparatuses permit dynamic or static tests using selectable current, voltage and angle or impedance parameters in a wide range. The test apparatuses are designed to be programable, so that the user can himself determine the test sequences if one does not wish to have recourse to existing test programs.
In these known test apparatuses, an external computer can be used in order to undertake calculations of theoretical tripping characteristics and to compare these theoretical characteristics with the measured actual tripping characteristics.
When measuring a tripping characteristic of a protective apparatus, for example a distance relay, in an impedance plane, either the modulus of the impedance is held constant and the angle is varied, or the angle is held constant and the modulus of the impedance is varied. It can happen in this measurement method that the line along which measurement is made--this is frequently a locating straight line-- intersects the actual tripping characteristic at a very acute angle, so that no clearly defined points of intersection are produced. Determining the actual tripping characteristic in this area can be performed only comparatively imprecisely, added to which a comparatively long time is required for these measurements carried out with the aid of iteration methods. In a further measurement method, an array of measurement points is laid over the impedance plane. The actual tripping characteristic can be determined to a rough approximation from these very time-consuming measurements.
During the respective measurements, the relay to be tested is decoupled from the power-line and cannot undertake its protective functions. Measurements which are more time-consuming and imprecise unnecessarily lengthen the time during which the protection cannot be fully ready for use.